1. Field of the Invention
The present invention relates to a sheet feeding device used for an image forming apparatus, such as a copying machine, a printer, a facsimile, a printing machine, and a multi function peripheral, and especially relates to a sheet feeding device, which is capable of securely separating and sending out one sheet at a time, such as a coated paper sheet.
2. Description of Related Art
The above-mentioned image forming apparatus includes a sheet feeding device, which sends out one sheet from a paper sheet bundle, into which several sheets are stacked, at a time with a sheet feeding roller. In such sheet feeding device, when a plurality of sheets is multi-fed, this multi feeding becomes a cause of a paper jam. When conveyance power is small, a miss feeding easily occurs. Therefore, the sheet feeding device is arranged to securely send one sheet at a time. That is, the miss feeding is prevented by securely sending out one topmost sheet of stacked sheets by increasing a friction coefficient between a sheet feed roller and a sheet. In addition, the sheet feeding device is arranged so that only one topmost sheet is sent out by pushing back a second and subsequent sheets with separation by a separation roller and a pad separation or by a separating claw so that no more than two sheets are send out.
This method is effective as long as only a general plain paper is being used. However, recently, applications of a copying machine or a printer have expanded and sheets with various paper qualities including a coated paper sheet have come to be used. Among these sheets is a case where an adherence force between the sheets at the time of stacking is strong and it is difficult to securely prevent the multi feeding in the above-mentioned sheet feeding device occurs.
Then, a method of providing a ventilation port on a side of sending direction of stacked sheets, blowing air toward a plurality of sheets on an upper part of the stacked sheets from this ventilation port and separating sheets by passing air between sheets is proposed.
However, the coated paper sheet has a characteristic of sheets adhering each other in a high humidity environment. A paper sheet bundle, which is strongly stuck together, becomes a heavy lump at low air velocity. Therefore, the adherence of sheets does not exfoliate and a sheet cannot be raised by blowing weak air from the side.
In order to resolve this, strengthening the blowing of air for raising a sheet can be considered. However, even if a flow of air is strengthened, the sheets are only pushed up largely and separation per sheet does not become good.
Accordingly, in Japanese Patent Application Publication No. 2004-043186, a configuration in which a sheet adsorption conveyance device, which adsorbs and conveys one sheet at a time by air suction from a bundle of sheets supported with a sheet stacking device, and a blower, which blows air to an upper part of a paper sheet bundle from a forward side of a sheet feeding direction, is proposed. By blowing the air from the forward side of the paper sheet bundle, several sheets on the upper part of the paper sheet bundle are raised, and a topmost sheet of the paper sheet bundle is adsorbed and conveyed by an adsorption conveyance device. When the topmost sheet is adsorbed by the adsorption conveyance device, the air from the forward side will function so that subsequent sheets separate.
In general, although a sheet feeding using such adsorption device has a tendency to become large comparing to a roller sheet feeding, it excels in a sheet feed ability. The reason is that the sheet feeding using such adsorption device is stable in the long run without effects of wear out and slip since it is not a friction separation and is comparatively unaffected by a sheet condition, such as paper kind.
However, ventilation only from the forward side of the paper sheet bundle is insufficient for the separation of sheets. Therefore, in Japanese Patent Application Publication No. 2003-182873, a ventilation port is formed in a side regulating member, which positions both sides of the paper sheet bundle. A configuration, which blows air from a side of the paper sheet bundle by this ventilation port, is proposed. The separation of sheets improves by the ventilation from side and forward.
Apart from that, since a blower from the side of the paper sheet bundle is arranged so that the center of the ascending and descending direction of the ventilation port comes almost to the upper surface of the paper sheet bundle, the upper end of the ventilation port comes above the upper surface of the paper sheet bundle. The sheet feeding device has the paper sheet bundle loaded on the drawer-type sheet feeding tray. When supplying sheets, a sheet feeding tray is pulled out and the sheets are supplied. The side regulating member with the ventilation port from the side is attached to the sheet feeding tray. A sheet adsorption conveyance device is attached to the image forming apparatus main body. Therefore, if a blower protrudes above the upper surface of the paper sheet bundle when pulling out a sheet feeding tray for the purpose of sheet supply, the blower interferes with the sheet adsorption conveyance device and becomes impossible to move. In Japanese Patent Application Publication No. 2003-182873, in order to avoid such a situation, the blower from the side is moved and provided near the rear end of the paper sheet bundle to not to interfere with the sheet adsorption conveyance device.
However, in the configuration of Japanese Patent Application Publication No. 2003-182873, when a sheet size is small, a problem that a case where the blower from the side cannot be used occurs.
The present invention solves such problems and an object of the present invention is to provide a sheet feeding device that is capable of being disposed a blower from the side right beneath the sheet adsorption conveyance section even for small size sheets and an image forming apparatus in which this sheet feeding device is provided.